Apparatus for classifying and cleaning a granular material



July 26, 1955 H. A. F. VON RECHENBERG 2,713,942

APPARATUS FOR CLASSIFYING AND CLEANING A GRANULAR MATERIAL Filed July 26, 1950 5 Sheets-Sheet 1 in venifa r-.

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APPARATUS FOR CLASSIFYING AND CLEANING A GRANULAR MATERIAL Filed July 26, 1950 5 Sheets-Sheet 2 in vg for:

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July 26, 1955 H. A. F. VON RECHENBERG 2,713,942

APPARATUS FOR CLASSIFYING AND CLEANING A GRANULAR MATERIAL Filed July 26. 1950 5 Sheets-Sheet 5 Fig. 6

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APPARATUS FOR CLASSIFYING AND CLEANING A GRANULAR MATERIAL Filed July 26, 1950 5 Sheets-Sheet 4 July 26, 1955 H. A. F. VON RECHENBERG 2,713,942

APPARATUS FOR CLASSIFYING AND CLEANING A GRANULAR MATERIAL Filed July 26, 1950 5 Sheets-Sheet 5 United States Patent 9 APPARATUS FOR CLASSIFYING AND CLEANING A GRANULAR MATERIAL Hans Albrecht Freiherr von Rechenberg, Koln-Marienburg, Germany, assignor to Kalker Trieurfabrik und Fabrik Gelochter Bleche Mayer & Cie., Heumar, Germany, a company Application July 26, 1950, Serial No. 176,012

Claims. (Cl. 209-22) My invention relatesto an apparatus for classifying and cleaning a granular material, such as grain or other seeds, and, more particularly, to an air aspirator equipped with screens for sifting grain.

It is an object of my invention to provide an improved apparatus of that kind requiring less power and floor space than prior apparatus for the same output and having a simplified design lending itself to manufacture at reduced costs.

In prior air aspirators for sifting and cleaning grain or other granular material, such material passes first into an air current carrying away dust, and other light particles and is then fed to a shaking and sifting device including 7 screens adapted to segregate stones, ears, coarse foreign matter and weed seeds. For this purpose there is provided a set of comparatively large screens arranged above each other and having perforations of different sizes adjustable knocking hammers being provided to prevent the perforations from getting congested.

The screens are oscillated by suitable shaking means, for instance by a freely swinging massadapted to oscillate the screen or screens with a frequency of 360 to 400 per minute and with an amplitude of about /2 inch. For an output of 1000 to 1200 kilograms per hour screens of a width of at least 24 inches and a length of 60 inches and a driving motor of multiple horsepower are required. The aspiration by the air current produced by a fan or blower mounted in the stationary supporting structure above the shaking frame will act on the material substantially near the entry of and near the discharge of the material only since the shaking frame is open on all of its sides whereby an intense efiect of the air aspira tion is limited to the two places mentioned.

I attain the above stated object of my invention by a plurality of improvements which while capable of individual use result in the greatest advance in the art if applied in combination with each other.

One of those improvements is such a design of the screen supporting structure as to guide the air current in a manner ensuring that the grain or other granular material will be subjected on its entire way from the point of entry up to the discharge to the air flow whereby the cleaning effect of the air current is substantially improved.

Another material improvement resides in the manner in which the oscillation of the screens takes place and is produced. I have discovered that a substantial increase of the frequency of oscillation coupled with a reduction in amplitude will cause the grain or other material to smoothly flow along and through the screens without congesting or clogging same. Since the increased frequency is of a similar magnitude to the number of revolutions of the fan or blower, the latter may be used to produce the oscillation.

Further features of my invention will appear from the description of some preferred embodiments of my invention with reference to the accompanying drawings and ice the features of novelty will be pointed out in the claims. In the drawings:

Fig. l is a diagrammatic longitudinal section of a grain cleaning apparatus provided with vibrating screens having an output of about 1000 kilograms per hour;

Fig. 2 is the cross-section taken along line A-B of Fig. 1;

Fig. 3 is the cross-section taken along line CD of Fig. 1 illustrating the fan and the screen-supporting box;

Fig. 4 represents an elevation of the apparatus shown in Fig. 1 on a smaller scale showing the means for mounting the screen-carrying box on its frame for oscillation;

Pig. 5 is an illustration similar to that of Fig. 4 of a modified suspension of the screen supporting box;

Fig. 6 is a longitudinal section through an apparatus similar to that of Fig. 1, indicating the air currents and the passage of the material through and along the screens within the screen box;

Fig. 7 illustrates a longitudinal section through a modi fled aspirator in which the shaft of the rotary fan constitutes the vibrator; and

Fig. 8 is a longitudinal section similar to that of Fig. 7 of an apparatus for classifying and cleaning granular material of a simplified type suitable for use in the chemical industry.

Within a stationary supporting frame 22 shown in Figs. 4 and 5 there is suspended at box 1 comprising a front wall 50, a rear wall 51, side walls 52 (Figs. 2 and 3), a bottom 53 and a top 54. This box encloses a set of screens arranged one above the other comprising a roughage screen 2, a kernel screen 3 and a sand screen 4 which are rigidly connected to the walls 50 and 52. A hopper 5 mounted on the top 54 of the box is adapted to feed the grain to be treated to the rear end of the roughage screen 2 which is slightly inclined towards the front wall 50 and shorter than the screens 3 and 4 thus leaving sufiicient unobstructed space within the box 1 for the drumshaped casing 6 of a rotary blower or fan having a shaft 55 journalled in the side walls 52 and carrying a rotary impeller 56. The fan casing 6 projects out of the box 1 and its outer portion has a discharge muzzle 57 while its side walls inside of the box 1 are provided with lateral intake openings 17. The two screens 3 and 4 having a width of about 12 inches and a length of about 26 inches are so shaped and disposed that their rear portions are inclined with respect to their front portions whereby the screening effect is improved and the feeding efliect exerted on the grain by the vibration is enhanced. Between the roughage screen 2 and the kernel screen 3 baffles 14 and 15 are interposed in order to guide the material in the manner illustrated in Fig. 6. The bafile plate 14 serves to guide the material dropping through the roughage screen 2 forwardly to a point where it is subjected to the intense aspirating effect of the air current entering through an air inlet opening 8 provided in the front wall 50 of the box 1. The bafile 15 serves the purpose of intercepting particles dropping out of the air current before the same enters the intake openings 17 of the fan and to guide such particles towards the central zone of the screen 3. Moreover, both baffies 14 and 15 serve to guide the aspirator air current. As will appear from Figs. 2 and 3, the screens and the baffles abut laterally the side walls 52 and are attached thereto. 7

Since the side walls 52 are substantially free of any openings, the air current produced by the fan enters the box in its entirety through the opening 8 and through an additional opening 9 provided in the front wall 50 between the screens 3 and 4, both openings 8 and 9 extending substantially across the whole width of the box. While the upper portion of the front wall 50 above the screen 2 is cut away to provide for an outlet for the roughage retained by the screen 2, such outlet is substantially closed by a wicket formed by a leather apron 16 which prevents the entry'of air while permitting a discharge of the surplus of roughage into a chute 18, Fig; 6. Hence, an intense air current will enter the box through the inlet openings 8 and 9 and will traverse the stream of material freely dropping from the front end of the baffle 14 and through the screen 3 and subject such stream to an efficient aspirating effect. It will appear from a consideration of Fig. 6 that, owing to a prevention of air by-passing the inlet openings 3 and 9 as was typical of prior air aspirators, the grain will be subjected to the effect of the air current indicated by thin lines in Fig. 6 during its entire passage through the screen box. V The different grades of the classified and cleaned material and the waste will leave the box through different discharge chutes 18, 19, 20 and 21 individually co-ordihated to the screens 2, 3, 4 and the bottom 53. In Fig. .1 an illustration of the chutes 18 and 20 has been omitted. Between the fan casing 6 and the front wall 50 there is journalled within the side walls 52a vibrator shaft 11 carrying a pulley adapted to be driven by a belt from an electric motor 10 or other prime mover mounted in the supporting frame 22, the vibrator shaft 11 being driven with a speed of about 2000 R. P. M. The shaft 11 is co-operatively connected with the fan shaft 55 by suitable means such as belt transmission indicated by dashdotted lines in Figs. 1 and 6. The discharge duct 57 of the fan is connected by a resilient hose 12 with theinlet of a cyclone separator 13 wherein the dust is separated from the air current.

' As shown in Fig. 4, the screenbox 1 is mounted on the supporting frame 22 by means of a pair of bent leaf springs 23 attached to the journals 24 which are mounted on the side walls 52 and accommodate the vibrator shaft 11'. In this manner the box 1 is so suspended as to be capable of performing the oscillatory motion imparted thereto by the vibrator relative to the supporting frame 22 and the stationary cyclone separator 13. In the embodiment shown in Fig. 5 I have shown another suspension more suitable for larger types of my novel aspirator. In this embodiment the springs 25 are attached tobrackets 58 fixed to the side walls 52 of the box 1.

'While the chute 19 co-ordinated to and arranged at the rear end of the screen 3 extends through a lateral opening 59 provided in one of the side walls 52, it is .to be understood that such opening 59 is made as small as possible and may be closed by a leather apron similar to an apron 16 to limit the entry of air therethrough to a minimum. The same is true of the chutes 20 and 21.

The vibrator shaft 11 is so, asymmetrically shaped as to have its center of gravity off-set from its axis of rotation whereby a vibration is produced by the centrifugal force.

From the foregoing description of some embodiments of my invention with reference to Figs. 1 to 6 it will appear that the vibrating screen support is formed by a box which is provided with inlets for the air current at its frontwall only, the side walls being substantially free of air intake openings whereby the grain or other seed during its entire passage from the feeding point near the front up to the rear discharge chutes is subjected to the aspiration effect producedby the air current sucked in by the fan and'discharged at the rear of the box. Owing to this arrangement the space in which an efficient aspirat ing effect is exerted on the material is greatly increased compared with prior apparatus in which such an effect was obtained at the places of the entry and discharge only since the air sucked in could enter from all sides and, therefore, was concentrated but at a few points to the extent required for a satisfactory aspirating function. In my improved apparatus the air set in motion by the aspirator is compelled to produce a powerful current not weakened by the effect of by-passed air, such current traversing the stream of grain dropping upon and through the screens. Obviously, this will enhance the aspirating 4 effect regarding both the quantity of the material treated and the quality'of the cleaning effect. Consequently the same cleaning effect is attainable with a much smaller fan consuming less power.

This advance in the art may be further enhanced by the mounting of the aspirator within the vibrating screen box itself. This will reduce the idle space, the length of the air path and the frictional resistance offered to the air by the walls and will thus lead to a further reduction of power consumption.

Another feature of novelty serving to reduce the'dimensions and the power consumption of an air aspirator and classifier having a given output resides in the new method of operating the vibrator at a frequency exceeding 1500 per minute and with a minute amplitude. Owing to this novel method of operating the screens, the screening effect is substantially improved whereby the output of a screen of a given size is multiplied compared with the prior shaking screens.

While it is known in the art that by increasing the frequency of the shaking motion the output of a screen set can be improved, a very definite limitation was placed on such increase of the speed of operation of prior classifiers by the consequent agitation of the mass of grain fed to the screens. It was found that when the frequency of the shaking motion of the screens reached a predetermined limit, the mass of grains was subjected 'to such a vehement agitation that it did no longer pass through the screens but passed across the same constituting a loose mass in which the individual kernels were performing a dancing or gyrating motion preventing them from finding an opening in the screens for passage therethrough. Therefore, the shaking screens were operated in practice at a speed far below the afore-described agitating speed limit. The exact frequency at which the agitating limit is reached depends on the nature of the material and. therefore, cannot be definitely stated in figures, but it can be easily determined by a simple experiment. Because of the phenomenon of the agitating limit it was the general practice to prescribe a speed of operation for each size and type of classifiers which was far below the frequency which I prefer to use.

My experiments had the surprising result to show that when the frequency of the screen oscillation is increased far above the agitating limit, the amplitude being at the same time substantially reduced, the efficiency of operation is materially improved. While an increase of the frequency of oscillation will first produce the well known agitation of the mass of grains and the consequent reduction of the output, such agitation or dancing or gyrating motion of the kernels or particles will disappear upon a further increase of frequency and the material will smoothly pass along and through the screen, such smooth motion resulting in a multiplied output compared with the best results obtainable in the prior art. The smooth flow of the granular material through the classifier re sulting from a vibration at a frequency exceeding the agitating limit may be explained by the fact that the impulses imparted to the kernels by the vibrating screens are so related to the momentum and the acceleration of the particles that the kernels cease to dance or gyrate and are kept in a more or less calm floating condition, it being necessary of course to adapt the magnitude of frequency and amplitude to the size of the screen openings and to the nature of the material to be classified. A simple experiment, however, will show the agitating speed limit and will teach how far the frequency must be increased above such speed limit. I have found, for instance, that where a classifier was operated by a shaker at a frequency of 360 to 400 per minute in the prior art I vibrate such screens at a speed of 1700 to 2500 R. P. M. with an amplitude of less than 1 millimeter. The afore described reaction of the material to an increase of the frequency of oscillation of the screens will clearly illustrate the basic distinction between the prior art shaker and'the high speed vibration of the present invention.

The larger output per square inch of screen surface makes it possible to run a much larger quantity of grain, for instance, five times as much grain through a classifying aspirator of a given size when the same is constructed in accordance with my invention. Contrariwise, a given output may be obtained with an apparatus of a much smaller size compared with the prior classifying aspirators. Thus it is possible, for instance, with screens of a size of 12 inches by 26 inches to handle the same amount of grain per hour as could be formerly handled by screens of a size of 24 inches by 60 inches. The reduction in size results in a corresponding reduction of power consumption. While with the old design a motor having multiple horsepower was required, the apparatus designed in accordance with my invention being capable of the same output requires a motor of lessthan l horsepower.

The basically different reaction of the granular material to the shaking impulses produced in the prior apparatus, on the one hand, and to the vibrations produced in my novel apparatus, on the other hand, was another advantage reflecting on the simplicity of the redesigned classifier. The screens vibrating at a frequency far above the critical agitating limit do no longer tend to get congested but will remain in a condition in which their holes are kept open. Therefore, no special provision of means for continually cleaning the screens, such as knocking hammers or the like, are required. The elimination of such means will further simplify the design and reduce the movable masses and will save power.

The vibrator characterized by its high frequency of operation far above the critical agitating frequency and by its reduced amplitude and the guidance of the aspiration air flow with respect to the screens constitute features of novelty which may be used individually as such to improve the function of the prior apparatus, but by the combination of both features I obtain a sensational advance relative to the size, power consumption and output of my novel classifying aspirator. Because of the reduced amplitude and the small power consumption of the vibrator, both the vibrator and the fan may be accommodated within the screen box in spite of the reduced size of the latter.

The positive guidance of the flow of air from the inlets 8, 9 along the screens 3 and 4 permits to considerably reduce the quantity of air to be fed by the fan. Therefore, the size of the fan may be reduced whereby its accommodation within the screen box is facilitated.

In order to make full use of the reduction of the size of the entire apparatus, I have connected the same with the cyclone separator 13 through the flexible hose 12. Obviously, all of these measures will greatly facilitate the accommodation of the entire grain cleaning plant and Will reduce the floor space required therefor.

As will appear from Figs. 1 and 6 the vibrator shaft 11, producing the centrifugal forces imparting oscillation to the screen box 1, and the fan 6, 56, which preferably is, but need not be mounted within the box 1, may be driven at similar speeds or at the same speed. A further improvement, however, may be obtained by combining the two shafts 11 and 55 in a single shaft serving both functions, that of the fan shaft and that of the vibrator shaft. Such structure is illustrated in Figs.7 and 8.

The air aspirator equipped with screens shown in Fig. 7 differs from that shown in Figs. 1 and 6 substantially by the omission of shaft 11, the impeller shaft 24 of the fan serving as vibrator shaft and, for that purpose, being shaped asymmetrically whereby its center of gravity is ofi-set from its axis of rotation. Moreover, the fan shaft 24 is moved closer to the center of the screen box 1' and is driven by a belt transmission from an electric motor mounted below the vibrating screen box within the supporting frame indicated in Fig. 7 by dash-dotted lines. In front of the intake openings 8' and 9 provided in e the front wall of the box 1' inclined covers are provided to prevent kernels from jumping out of the box. The flow of grain'down the slightly inclined chute 19 similar to chute 19 in Fig. 1 is greatly promoted by the vibration produced by the fan 6'.

The elimination of shaft 11 results in a further reduction of weight and space whereby the classifying aspirator may be constructed in an even more compact manner without detracting from its efiiciency. The reduction in weight reduces the energy required to impart the vibra tion to the box 1. Hence, the driving motor 10' may be made less powerful than the motor 10 in Fig. 1.

Obviously, the impeller shaft having the combined function of serving to oscillate a set of screens and of producing a flow of air may be used in seed grading apparatus of the type described and also in other classifiers for granular material.

The asymmetrical shape of the impeller shaft 24 may be produced in various ways, for instance by milling lateral recesses 37 in the shaft as shown in Fig. 8 or by attaching small fly weights on the shaft or the impeller. While in the embodiments described herein the fan or blower produces the aspirating air current by suction, such current may be produced just as well by blowing the air current into the box 1. Also it is immaterial for certain aspects of my invention for what purpose the vibration is produced by the impeller shaft since, whatever that purpose might be, the elimination of a separate vibrator will result in a substantial advance in the art. Hence, my improved vibrating fan or blower is applicable to numerous material-processing apparatus including vibrating elements and requiring a flow of air as used in various industries such as the chemical industry, the food processing industry, steel mills, mines, cotton and other mills, agriculture etc. In all of those industries the need arises of combining an oscillating screening or transporting device with means for removing dust by an air current. This is true for instance Where granular material is to be classifled by means of oscillating screens or the like and where precaution must be taken to remove the resulting dust. The same is true with transporting chute such as the chute 19 illustrated in Fig. 3 which must be oscillated in order to permit the material to flow therein and, because of such oscillation, is liable to generate dust. The granular material to be treated may be grain or seeds of all kind, disintegrated minerals or coal. An important application of my invention is the processing of carbide in which the dust separated from the air current is collected and in which the air is circulated from the cyclone separator back to the screen box. My invention is also applicable to machines for polishing farina including vibrating elements and an aspirator.

While the embodiments of my invention illustrated in Figs. 1 to 7 are designed for the purpose of classifying and cleaning grain, Fig. 8 illustrates a similar apparatus equipped with but two screens 27 and 28 serving to treat granular material made up of particles of various sizes and of dust such as is frequently encountered in the chemical industry. The granular material is fed into the vibratory screen box 26 through a hopper 25. The coarsest particles are segregated by the coarse screen 27. The rest passes under guidance by a baffle 40 to a finer screen 28 and, on its way, is subjected to a flow of air entering an opening 31protected by an inclined cover plate 32. The asymmetrical impeller shaft 36 journalled in the side wall of the screen box 26 is driven by an electric motor 34 mounted in the supporting frame 33 through a transmission belt 35. A material having medium sized particles is discharged through an opening 29 while the finest material is discharged through an opening provided in the bottom of the screen box 26. The dust carried along by the air current is separated therefrom by a cyclone separator 39 attached to the fan or blower 30 by a flexible hose 38. The screen box 26 is mounted on the supporting frame 33 in the manner illustrated in Figs.'4 or 5.

While I have described my invention with reference to a'number of preferred embodiments thereof I wish it to be clearly understood that it is in no way limited to such embodiments but is capable of numerous modifications within the scope of the appended claims.

What I claim is:

1. Apparatus for cleaning and classifying intermixed granular materials, comprising a frame, a generally boxshaped enclosure, means for resiliently supporting said enclosure on said frame, said enclosure being closed on its sides and having a front wall, a rear wall, and a bottom wall, a screen mounted in said enclosure and extending from one side thereof to the other, said screen being fixed to said side walls and being downwardly inclined from the front wall of the enclosure toward the rear wall thereof, means for delivering granular material to a point above the front end of said screen whence said material falls by gravity toward said screen, the front wall of said enclosure having an opening therein above said screen and below said delivery point to admit air to the enclosure, a fan mounted in said enclosure above said screen at some distance rearwardly of the front wall of said enclosure and operative to suck air through said opening and through the falling material to carry away fines and light debris, and means for vibrating said enclosure.

2. Apparatus for cleaning and classifying intermixed granular materials, comprising a frame, a generally boxshaped enclosure mounted on said frame, said enclosure being closed on its sides and having a front wall, a rear Wall and a bottom wall, a screen mounted in said enclosure and extending from one side thereof to the other and from the front wall of the enclosure toward the rear wall thereof, -means for delivering granular material to a point above the front end of said screen whence said material falls by gravity toward said screen, the front 1 wall of said enclosure having two openings therein, one above said screen and below said delivery point, and the other below said screen, said openings serving to admit air to the enclosure, a fan mounted in said enclosure above said screen at some distance rearwardly of the front wall of said enclosure and operative to suck air through both said openings and through the falling material to carry away fines and light debris, resilient means for supporting said enclosure on said frame, and means for vibrating said enclosure. 7

3. Apparatus for.cleaning and classifying intermixed granular materials comprising a frame, a generally boxshaped enclosure closed on its sides and having a front wall, a rear wall, and a bottom wall, resilient means supporting saidtenclosureon said frame, a screen mounted in said enclosure and extending from one side thereof to the other and from the front wall of the enclosure toward the rear wall thereof, means for delivering granular material to a point above the front end of said screen whence said material falls by gravity toward said screen,

the front wall of said enclosure having an opening therein above said screen and below said delivery point to admit air to the enclosure, a fan mounted in said enclosure above said screen at some distance rearwardly of the front wall of said enclosure and operative to suck air through said opening and through the falling material to carry away fines and light debris, said enclosure having a wall above said screen extending rearwardly from said delivery point to form with said screen and with the side walls of said enclosure a ductthrough which the air sucked by said fan travels lengthwise of said screen, and means for vibrating said enclosure to cause material falling on said screen to move toward the rear of said box.

4. Apparatus for cleaning and classifying intermixed granular materials comprising a frame, a generally boxshaped enclosure closed on its sides and having a front wall, a rear wall, and a bottom wall, resilient means supporting said enclosure on said frame, a screen mounted in said enclosure and extending from one side thereof to the other and from the front wall of the enclosure toward the rear wall thereof, means for delivering granular mate-- rial to a point above the front end of said screen whence said material falls by gravity toward said screen, the front wall of said enclosure having an opening therein above said screen and below said delivery point to admit air to the enclosure, a rotary fan mounted in said enclosure above said screen at some distance rearwardly of the front wall of said enclosure and operative to suck air through said opening and through the falling material to carry away fines and light debris, said enclosure having a wall above said screen extending rearwardly from said delivery point to form with said screen and with the side walls of said enclosure a duct through which the air sucked by said fan travels lengthwise of said screen, and means for vibrating said enclosure to cause material falling on said screen to move toward the rear of said box, and means for actuating said vibrating means and for rotating said fan simultaneously.

5. Apparatus for cleaning and classifying cereal grains comprising a frame, a generally box-shaped enclosure closed on its sides and having a front wall, a rear wall, and a bottom wall, resilient means supporting said enclosure on said frame, a screen mounted in said enclosure and extending from one side thereof to the other and from the front wall of the enclosure toward the rear wall thereof, means for delivering cereal grains to a point above the front end of said screen whence said grains fall by gravity toward said screen, the front wall of said enclosure having an opening therein above said screen and below said delivery point to admit air to the enclosure, a fan mounted in said enclosure above said screen at some distance rearwardly of the front wall of said enclosure and operative to suck air through said opening and through the falling grains to carry away fines and light debris, said enclosure having a wall above said screen extending rearwardly from said delivery point to form with said screen and with the side walls of said enclosure a duct through which the air sucked by said fan travels lengthwise of said screen, and means for vibrating said enclosure at a rate exceeding 1500 oscillations per minute and at an amplitude in the order of about 1 mm.

6. Apparatus for cleaning and classifying intermixed granular materials comprising a frame, a generally boxshaped enclosure closed on its sides and having a front wall, a rear wall, and a bottom wall, resilient means supporting said enclosure on said frame, a screen mounted in said enclosure and extending from one side thereof to the other and from the front wall of the enclosure toward the rear wall thereof, means for delivering granular material to a point above the front end of said screen whence said material falls by gravity toward said screen, the front wall of said enclosure having an opening therein above said screen and below said delivery point to admit air to the enclosure, a fan mounted in said enclosure above said screen at some distance rearwardly of the front wall of said enclosure and operative to suck air through said opening and through the falling material to carry away fines and light debris, said enclosure having a wall above said screen extending rearwardly from said delivery point to form with said screen and with the side walls ofsaid enclosure a duct through which the air sucked by said fan travels lengthwise of said screen, a rotary shaft journaled in said enclosure and on which said fan is mounted, and means on said shaft operative upon rotation of said shaft for vibrating said enclosure to cause material on said screen to move toward the rear of said enclosure, and means for rotating said shaft.

7. Apparatus for cleaning and classifying intermixed granular materials comprising a frame, a generally boxshaped enclosure closed on its sides and having a front wall, a rear wall, and a bottom wall, resilient means supporting said enclosure on said frame, a screen mounted in said enclosure and extending from one side thereof to the other and from the front wall of the enclosure toward the rear wall thereof, means for delivering granular material to a point above the front end of said screen whence said material falls by gravity toward said screen, the front wall of said enclosure having an opening therein above said screen and below said delivery point to admit air to the enclosure, a fan mounted in said enclosure above said screen at some distance rearwardly of the front wall of said enclosure and operative to suck air through said opening and through the falling material to carry away fines and light debris, said enclosure having a wall above said screen extending rearwardly from said delivery point to form with said screen and with the side walls of said en-- closure a duct through which the air sucked by said fan travels lengthwise of said screen, said fan including a rotary element having its center of gravity offset from its axis of rotation, means connecting said rotary element to said enclosure to vibrate said enclosure on rotation of said fan, and means for rotating said fan.

8. Apparatus for cleaning and classifying intermixed granular materials, comprising a frame, a generally boxshaped enclosure closed on its sides and having a front wall, a rear wall, and a bottom wall, a plurality of screens mounted in said enclosure, one above the other, and each extending from one side of the enclosure to the other and from the front wall of said enclosure toward the rear wall thereof, the coarsest of said screens being uppermost and said screens being progressively finer downwardly of said enclosure, means for delivering granular material to a point above the front end of the uppermost of said screens whence said material falls by gravity toward said uppermost screen, the front wall of said, enclosure having an opening therein above each of a plurality of said screens to admit air to said enclosure, the uppermost of said openings being below said delivery point, a fan mounted in said enclosure above said uppermost screen at some distance rearwardly of the front wall of said enclosure and operative to suck air through said openings, a wall in said enclosure above said uppermost screen to form with said uppermost screen a duct through which the air flows from said uppermost opening and through the falling material lengthwise of said uppermost screen to said fan, resilient means for supporting said enclosure on said frame, and means for vibrating said enclosure.

9. Apparatus for cleaning and classifying intermixed granular materials, comprising a frame, a generally boxshaped enclosure closed on its sides and having a front wall, a rear wall, and a bottom wall, a plurality of screens mounted in said enclosure, one above the other, and each extending from one side of the enclosure to the other and from the front Wall of said enclosure toward the rear wall thereof, the coarsest of said screens being uppermost and said screens being progressively finer downwardly of said enclosure, means for delivering granular material to a point above the front end of the uppermost of said screens whence said material falls by gravity toward said uppermost screen, the front wall of said enclosure having an opening therein above each of a plurality of said screens to admit air to said enclosure, the uppermost of said openings being below said delivery point, a fan mounted in said enclosure above said uppermost screen at some distance rearwardly of the front wall of said enclosure and operative to suck air through said openings,

a wall in said enclosure above said uppermost screen to form with said uppermost screen a duet through which the air flows from said uppermost opening and through the falling material lengthwise of said uppermost screen to said fan, resilient means for supporting said enclosure on said frame, said fan including a rotary element having its center of gravity offset from its axis of rotation, and means connecting said rotary element to said enclosure to vibrate said enclosure on rotation of said fan.

10. Apparatus for cleaning and classifying intermixed granular materials, comprising a frame, a generally boxshaped enclosure closed on its sides and having a front wall, a rear wall, and a bottom wall, a plurality of screens mounted in said enclosure, one above the other, and each extending from one side of the enclosure to the other and from the front wall of said enclosure toward the rear wall thereof, the coarsest of said screens being uppermost and said screens being progressively finer downwardly of said enclosure, means for delivering granular material to a point above the front end of the uppermost of said screens whence said material falls by gravity toward said uppermost screen, the front wall of said enclosure having an opening therein above each of a plurality of said screens to admit air to said enclosure, the uppermost of said openings being below said delivery point, a fan mounted in said enclosure above said uppermost screen at some distance rearwardly of the front wall of said enclosure and operative to suck air through said openings, a wall in said enclosure above said uppermost screen to form with said uppermost screen a duct through which the air flows from said uppermost opening and through the falling material lengthwise of said uppermost screen to said fan, resilient means for supporting said enclosure on said frame, and means for vibrating said enclosure, the two lowermost of said screens, at least, being inclined downwardly at least at their rear portions.

References Cited in the file of this patent UNITED STATES PATENTS heading entitled New Vibrating Screen." Scientific Library.)

Handbook of Mineral Dressing, by Taggart. Copyright in 1945. Pages 7-44 and 7-45 relied on. (Copy in Div. 55.)

(Copy in 

